The present invention relates to a switch for controlling the operation of an electrical appliance.
In certain types of electrical slide switches, the movable contact member is cantilevered for pivotal movement to make and break electrical connection with the fixed contact(s). For various reasons, a movable contact member of an extended length is needed, in which case the contact member may become slack after prolonged use, thereby failing to provide the necessary contact pressure. An example of this type of electrical switch is disclosed in U.S. Pat. No. 6,281,482.
The invention seeks to mitigate or at least alleviate such a problem by providing an improved electrical switch.
According to the invention, there is provided an electrical switch comprising a casing, and at least one fixed contact and a elongate resiliently deformable movable contact member in the casing, said contact member having opposite first and second sides. The switch includes a switching member supported by the casing in sliding contact on the first side of and with an intermediate part of the contact member to cause the contact member to pivot against its resilience for making and breaking electrical connection with the fixed contact. The contact member includes a fixed end at which it is cantilevered for pivotal movement and a free end for contact with the fixed contact. Resilient means is provided acting resiliently upon the second side of the contact member to maintain the sliding contact of the contact member with the switching member.
Preferably, at least two said fixed contacts are included, and the free end of the movable contact member is divided into contact prongs arranged to contact with the fixed contacts respectively.
More preferably, each contact prong includes an individual intermediate part with which the switching member is in sliding contact.
Further more preferably, the switching member includes parallel tracks, each having relatively protruding and non-protruding sections along its length, in sliding contact with the intermediate parts of the contact prongs respectively, thereby providing a number of switching combinations between the contact prongs and the fixed contacts according to the relative position of the switching member.
It is preferred that the or each intermediate part comprises a bend towards the switching member.
In a first preferred embodiment, the resilient means comprise respective springs acting upon the contact prongs of the movable contact member.
More preferably, each spring comprises a compression coil spring.
It is preferred that each spring acts upon the respective contact prong at a position on the same side of the corresponding intermediate part as the fixed end of the movable contact member.
In a second preferred embodiment, the resilient means comprises a lever spring having a fixed end at which it is cantilevered for pivotal movement and a free end divided into prongs acting upon the contact prongs of the movable contact member respectively.
More preferably, the spring is cantilevered by the same support as the movable contact member.
It is preferred that the spring overlaps with the movable contact member in a double layered configuration, having a substantially complementarily shape to lie fittingly against the contact member.
It is preferred that the spring has an overall length in the range from 50% to 100% of that of the movable contact member.